Adding upstream version 4:7.4.7.upstream/4%7.4.7upstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 824 insertions, 0 deletions

diff --git a/vcl/skia/SkiaHelper.cxx b/vcl/skia/SkiaHelper.cxx
new file mode 100644
index 000000000..84c40baff
--- /dev/null
+++ b/vcl/skia/SkiaHelper.cxx
@@ -0,0 +1,824 @@
+/* -*- Mode: C++; tab-width: 4; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
+/*
+ * This file is part of the LibreOffice project.
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+#include <sal/config.h>
+
+#include <string_view>
+
+#include <vcl/skia/SkiaHelper.hxx>
+
+#if !HAVE_FEATURE_SKIA
+
+namespace SkiaHelper
+{
+bool isVCLSkiaEnabled() { return false; }
+
+} // namespace
+
+#else
+
+#include <rtl/bootstrap.hxx>
+#include <vcl/svapp.hxx>
+#include <desktop/crashreport.hxx>
+#include <officecfg/Office/Common.hxx>
+#include <watchdog.hxx>
+#include <skia/zone.hxx>
+#include <sal/log.hxx>
+#include <driverblocklist.hxx>
+#include <skia/utils.hxx>
+#include <config_folders.h>
+#include <osl/file.hxx>
+#include <tools/stream.hxx>
+#include <list>
+#include <o3tl/lru_map.hxx>
+
+#include <SkBitmap.h>
+#include <SkCanvas.h>
+#include <SkEncodedImageFormat.h>
+#include <SkPaint.h>
+#include <SkSurface.h>
+#include <SkGraphics.h>
+#include <GrDirectContext.h>
+#include <SkRuntimeEffect.h>
+#include <SkOpts_spi.h>
+#include <skia_compiler.hxx>
+#include <skia_opts.hxx>
+#include <tools/sk_app/VulkanWindowContext.h>
+#include <tools/sk_app/MetalWindowContext.h>
+#include <fstream>
+
+namespace SkiaHelper
+{
+static OUString getCacheFolder()
+{
+    OUString url("${$BRAND_BASE_DIR/" LIBO_ETC_FOLDER
+                 "/" SAL_CONFIGFILE("bootstrap") ":UserInstallation}/cache/");
+    rtl::Bootstrap::expandMacros(url);
+    osl::Directory::create(url);
+    return url;
+}
+
+static void writeToLog(SvStream& stream, const char* key, const char* value)
+{
+    stream.WriteCharPtr(key);
+    stream.WriteCharPtr(": ");
+    stream.WriteCharPtr(value);
+    stream.WriteChar('\n');
+}
+
+uint32_t vendorId = 0;
+
+#ifdef SK_VULKAN
+static void writeToLog(SvStream& stream, const char* key, std::u16string_view value)
+{
+    writeToLog(stream, key, OUStringToOString(value, RTL_TEXTENCODING_UTF8).getStr());
+}
+
+static OUString getDenylistFile()
+{
+    OUString url("$BRAND_BASE_DIR/" LIBO_SHARE_FOLDER);
+    rtl::Bootstrap::expandMacros(url);
+
+    return url + "/skia/skia_denylist_vulkan.xml";
+}
+
+static uint32_t driverVersion = 0;
+
+static OUString versionAsString(uint32_t version)
+{
+    return OUString::number(version >> 22) + "." + OUString::number((version >> 12) & 0x3ff) + "."
+           + OUString::number(version & 0xfff);
+}
+
+static std::string_view vendorAsString(uint32_t vendor)
+{
+    return DriverBlocklist::GetVendorNameFromId(vendor);
+}
+
+// Note that this function also logs system information about Vulkan.
+static bool isVulkanDenylisted(const VkPhysicalDeviceProperties& props)
+{
+    static const char* const types[]
+        = { "other", "integrated", "discrete", "virtual", "cpu", "??" }; // VkPhysicalDeviceType
+    driverVersion = props.driverVersion;
+    vendorId = props.vendorID;
+    OUString vendorIdStr = "0x" + OUString::number(props.vendorID, 16);
+    OUString deviceIdStr = "0x" + OUString::number(props.deviceID, 16);
+    OUString driverVersionString = versionAsString(driverVersion);
+    OUString apiVersion = versionAsString(props.apiVersion);
+    const char* deviceType = types[std::min<unsigned>(props.deviceType, SAL_N_ELEMENTS(types) - 1)];
+
+    CrashReporter::addKeyValue("VulkanVendor", vendorIdStr, CrashReporter::AddItem);
+    CrashReporter::addKeyValue("VulkanDevice", deviceIdStr, CrashReporter::AddItem);
+    CrashReporter::addKeyValue("VulkanAPI", apiVersion, CrashReporter::AddItem);
+    CrashReporter::addKeyValue("VulkanDriver", driverVersionString, CrashReporter::AddItem);
+    CrashReporter::addKeyValue("VulkanDeviceType", OUString::createFromAscii(deviceType),
+                               CrashReporter::AddItem);
+    CrashReporter::addKeyValue("VulkanDeviceName", OUString::createFromAscii(props.deviceName),
+                               CrashReporter::Write);
+
+    SvFileStream logFile(getCacheFolder() + "/skia.log", StreamMode::WRITE | StreamMode::TRUNC);
+    writeToLog(logFile, "RenderMethod", "vulkan");
+    writeToLog(logFile, "Vendor", vendorIdStr);
+    writeToLog(logFile, "Device", deviceIdStr);
+    writeToLog(logFile, "API", apiVersion);
+    writeToLog(logFile, "Driver", driverVersionString);
+    writeToLog(logFile, "DeviceType", deviceType);
+    writeToLog(logFile, "DeviceName", props.deviceName);
+
+    SAL_INFO("vcl.skia",
+             "Vulkan API version: " << apiVersion << ", driver version: " << driverVersionString
+                                    << ", vendor: " << vendorIdStr << " ("
+                                    << vendorAsString(vendorId) << "), device: " << deviceIdStr
+                                    << ", type: " << deviceType << ", name: " << props.deviceName);
+    bool denylisted
+        = DriverBlocklist::IsDeviceBlocked(getDenylistFile(), DriverBlocklist::VersionType::Vulkan,
+                                           driverVersionString, vendorIdStr, deviceIdStr);
+    writeToLog(logFile, "Denylisted", denylisted ? "yes" : "no");
+    return denylisted;
+}
+#endif
+
+#ifdef SK_METAL
+static void writeSkiaMetalInfo()
+{
+    SvFileStream logFile(getCacheFolder() + "/skia.log", StreamMode::WRITE | StreamMode::TRUNC);
+    writeToLog(logFile, "RenderMethod", "metal");
+}
+#endif
+
+static void writeSkiaRasterInfo()
+{
+    SvFileStream logFile(getCacheFolder() + "/skia.log", StreamMode::WRITE | StreamMode::TRUNC);
+    writeToLog(logFile, "RenderMethod", "raster");
+    // Log compiler, Skia works best when compiled with Clang.
+    writeToLog(logFile, "Compiler", skia_compiler_name());
+}
+
+#if defined(SK_VULKAN) || defined(SK_METAL)
+static std::unique_ptr<sk_app::WindowContext> getTemporaryWindowContext();
+#endif
+
+static void checkDeviceDenylisted(bool blockDisable = false)
+{
+    static bool done = false;
+    if (done)
+        return;
+
+    SkiaZone zone;
+
+    bool useRaster = false;
+    switch (renderMethodToUse())
+    {
+        case RenderVulkan:
+        {
+#ifdef SK_VULKAN
+            // First try if a GrDirectContext already exists.
+            std::unique_ptr<sk_app::WindowContext> temporaryWindowContext;
+            GrDirectContext* grDirectContext
+                = sk_app::VulkanWindowContext::getSharedGrDirectContext();
+            if (!grDirectContext)
+            {
+                // This function is called from isVclSkiaEnabled(), which
+                // may be called when deciding which X11 visual to use,
+                // and that visual is normally needed when creating
+                // Skia's VulkanWindowContext, which is needed for the GrDirectContext.
+                // Avoid the loop by creating a temporary WindowContext
+                // that will use the default X11 visual (that shouldn't matter
+                // for just finding out information about Vulkan) and destroying
+                // the temporary context will clean up again.
+                temporaryWindowContext = getTemporaryWindowContext();
+                grDirectContext = sk_app::VulkanWindowContext::getSharedGrDirectContext();
+            }
+            bool denylisted = true; // assume the worst
+            if (grDirectContext) // Vulkan was initialized properly
+            {
+                denylisted
+                    = isVulkanDenylisted(sk_app::VulkanWindowContext::getPhysDeviceProperties());
+                SAL_INFO("vcl.skia", "Vulkan denylisted: " << denylisted);
+            }
+            else
+                SAL_INFO("vcl.skia", "Vulkan could not be initialized");
+            if (denylisted && !blockDisable)
+            {
+                disableRenderMethod(RenderVulkan);
+                useRaster = true;
+            }
+#else
+            SAL_WARN("vcl.skia", "Vulkan support not built in");
+            (void)blockDisable;
+            useRaster = true;
+#endif
+            break;
+        }
+        case RenderMetal:
+        {
+#ifdef SK_METAL
+            // First try if a GrDirectContext already exists.
+            std::unique_ptr<sk_app::WindowContext> temporaryWindowContext;
+            GrDirectContext* grDirectContext = sk_app::getMetalSharedGrDirectContext();
+            if (!grDirectContext)
+            {
+                // Create a temporary window context just to get the GrDirectContext,
+                // as an initial test of Metal functionality.
+                temporaryWindowContext = getTemporaryWindowContext();
+                grDirectContext = sk_app::getMetalSharedGrDirectContext();
+            }
+            if (grDirectContext) // Metal was initialized properly
+            {
+                // Try to assume Metal always works, given that Mac doesn't have such as wide range of HW vendors as PC.
+                // If there turns out to be problems, handle it similarly to Vulkan.
+                SAL_INFO("vcl.skia", "Using Skia Metal mode");
+                writeSkiaMetalInfo();
+            }
+            else
+            {
+                SAL_INFO("vcl.skia", "Metal could not be initialized");
+                disableRenderMethod(RenderMetal);
+                useRaster = true;
+            }
+#else
+            SAL_WARN("vcl.skia", "Metal support not built in");
+            useRaster = true;
+#endif
+            break;
+        }
+        case RenderRaster:
+            useRaster = true;
+            break;
+    }
+    if (useRaster)
+    {
+        SAL_INFO("vcl.skia", "Using Skia raster mode");
+        // software, never denylisted
+        writeSkiaRasterInfo();
+    }
+    done = true;
+}
+
+static bool skiaSupportedByBackend = false;
+static bool supportsVCLSkia()
+{
+    if (!skiaSupportedByBackend)
+    {
+        SAL_INFO("vcl.skia", "Skia not supported by VCL backend, disabling");
+        return false;
+    }
+    return getenv("SAL_DISABLESKIA") == nullptr;
+}
+
+bool isVCLSkiaEnabled()
+{
+    /**
+     * The !bSet part should only be called once! Changing the results in the same
+     * run will mix Skia and normal rendering.
+     */
+
+    static bool bSet = false;
+    static bool bEnable = false;
+    static bool bForceSkia = false;
+
+    // No hardware rendering, so no Skia
+    // TODO SKIA
+    if (Application::IsBitmapRendering())
+        return false;
+
+    if (bSet)
+    {
+        return bForceSkia || bEnable;
+    }
+
+    /*
+     * There are a number of cases that these environment variables cover:
+     *  * SAL_FORCESKIA forces Skia if disabled by UI options or denylisted
+     *  * SAL_DISABLESKIA avoids the use of Skia regardless of any option
+     */
+
+    bSet = true;
+    bForceSkia = !!getenv("SAL_FORCESKIA") || officecfg::Office::Common::VCL::ForceSkia::get();
+
+    bool bRet = false;
+    bool bSupportsVCLSkia = supportsVCLSkia();
+    if (bForceSkia && bSupportsVCLSkia)
+    {
+        bRet = true;
+        SkGraphics::Init();
+        SkLoOpts::Init();
+        // don't actually block if denylisted, but log it if enabled, and also get the vendor id
+        checkDeviceDenylisted(true);
+    }
+    else if (getenv("SAL_FORCEGL"))
+    {
+        // Skia usage is checked before GL usage, so if GL is forced (and Skia is not), do not
+        // enable Skia in order to allow GL.
+        bRet = false;
+    }
+    else if (bSupportsVCLSkia)
+    {
+        static bool bEnableSkiaEnv = !!getenv("SAL_ENABLESKIA");
+
+        bEnable = bEnableSkiaEnv;
+
+        if (officecfg::Office::Common::VCL::UseSkia::get())
+            bEnable = true;
+
+        // Force disable in safe mode
+        if (Application::IsSafeModeEnabled())
+            bEnable = false;
+
+        if (bEnable)
+        {
+            SkGraphics::Init();
+            SkLoOpts::Init();
+            checkDeviceDenylisted(); // switch to raster if driver is denylisted
+        }
+
+        bRet = bEnable;
+    }
+
+    if (bRet)
+        WatchdogThread::start();
+
+    CrashReporter::addKeyValue("UseSkia", OUString::boolean(bRet), CrashReporter::Write);
+
+    return bRet;
+}
+
+static RenderMethod methodToUse = RenderRaster;
+
+static bool initRenderMethodToUse()
+{
+    if (const char* env = getenv("SAL_SKIA"))
+    {
+        if (strcmp(env, "raster") == 0)
+        {
+            methodToUse = RenderRaster;
+            return true;
+        }
+#ifdef MACOSX
+        if (strcmp(env, "metal") == 0)
+        {
+            methodToUse = RenderMetal;
+            return true;
+        }
+#else
+        if (strcmp(env, "vulkan") == 0)
+        {
+            methodToUse = RenderVulkan;
+            return true;
+        }
+#endif
+        SAL_WARN("vcl.skia", "Unrecognized value of SAL_SKIA");
+        abort();
+    }
+    methodToUse = RenderRaster;
+    if (officecfg::Office::Common::VCL::ForceSkiaRaster::get())
+        return true;
+#ifdef SK_METAL
+    methodToUse = RenderMetal;
+#endif
+#ifdef SK_VULKAN
+    methodToUse = RenderVulkan;
+#endif
+    return true;
+}
+
+RenderMethod renderMethodToUse()
+{
+    static bool methodToUseInited = initRenderMethodToUse();
+    if (methodToUseInited) // Used just to ensure thread-safe one-time init.
+        return methodToUse;
+    abort();
+}
+
+void disableRenderMethod(RenderMethod method)
+{
+    if (renderMethodToUse() != method)
+        return;
+    // Choose a fallback, right now always raster.
+    methodToUse = RenderRaster;
+}
+
+// If needed, we'll allocate one extra window context so that we have a valid GrDirectContext
+// from Vulkan/MetalWindowContext.
+static std::unique_ptr<sk_app::WindowContext> sharedWindowContext;
+
+static std::unique_ptr<sk_app::WindowContext> (*createGpuWindowContextFunction)(bool) = nullptr;
+static void setCreateGpuWindowContext(std::unique_ptr<sk_app::WindowContext> (*function)(bool))
+{
+    createGpuWindowContextFunction = function;
+}
+
+GrDirectContext* getSharedGrDirectContext()
+{
+    SkiaZone zone;
+    assert(renderMethodToUse() != RenderRaster);
+    if (sharedWindowContext)
+        return sharedWindowContext->directContext();
+    // TODO mutex?
+    // Set up the shared GrDirectContext from Skia's (patched) Vulkan/MetalWindowContext, if it's been
+    // already set up.
+    switch (renderMethodToUse())
+    {
+        case RenderVulkan:
+#ifdef SK_VULKAN
+            if (GrDirectContext* context = sk_app::VulkanWindowContext::getSharedGrDirectContext())
+                return context;
+#endif
+            break;
+        case RenderMetal:
+#ifdef SK_METAL
+            if (GrDirectContext* context = sk_app::getMetalSharedGrDirectContext())
+                return context;
+#endif
+            break;
+        case RenderRaster:
+            abort();
+    }
+    static bool done = false;
+    if (done)
+        return nullptr;
+    done = true;
+    if (createGpuWindowContextFunction == nullptr)
+        return nullptr; // not initialized properly (e.g. used from a VCL backend with no Skia support)
+    sharedWindowContext = createGpuWindowContextFunction(false);
+    GrDirectContext* grDirectContext
+        = sharedWindowContext ? sharedWindowContext->directContext() : nullptr;
+    if (grDirectContext)
+        return grDirectContext;
+    SAL_WARN_IF(renderMethodToUse() == RenderVulkan, "vcl.skia",
+                "Cannot create Vulkan GPU context, falling back to Raster");
+    SAL_WARN_IF(renderMethodToUse() == RenderMetal, "vcl.skia",
+                "Cannot create Metal GPU context, falling back to Raster");
+    disableRenderMethod(renderMethodToUse());
+    return nullptr;
+}
+
+#if defined(SK_VULKAN) || defined(SK_METAL)
+static std::unique_ptr<sk_app::WindowContext> getTemporaryWindowContext()
+{
+    if (createGpuWindowContextFunction == nullptr)
+        return nullptr;
+    return createGpuWindowContextFunction(true);
+}
+#endif
+
+static RenderMethod renderMethodToUseForSize(const SkISize& size)
+{
+    // Do not use GPU for small surfaces. The problem is that due to the separate alpha hack
+    // we quite often may call GetBitmap() on VirtualDevice, which is relatively slow
+    // when the pixels need to be fetched from the GPU. And there are documents that use
+    // many tiny surfaces (bsc#1183308 for example), where this slowness adds up too much.
+    // This should be re-evaluated once the separate alpha hack is removed (SKIA_USE_BITMAP32)
+    // and we no longer (hopefully) fetch pixels that often.
+    if (size.width() <= 32 && size.height() <= 32)
+        return RenderRaster;
+    return renderMethodToUse();
+}
+
+sk_sp<SkSurface> createSkSurface(int width, int height, SkColorType type, SkAlphaType alpha)
+{
+    SkiaZone zone;
+    assert(type == kN32_SkColorType || type == kAlpha_8_SkColorType);
+    sk_sp<SkSurface> surface;
+    switch (renderMethodToUseForSize({ width, height }))
+    {
+        case RenderVulkan:
+        case RenderMetal:
+        {
+            if (GrDirectContext* grDirectContext = getSharedGrDirectContext())
+            {
+                surface = SkSurface::MakeRenderTarget(grDirectContext, SkBudgeted::kNo,
+                                                      SkImageInfo::Make(width, height, type, alpha),
+                                                      0, surfaceProps());
+                if (surface)
+                {
+#ifdef DBG_UTIL
+                    prefillSurface(surface);
+#endif
+                    return surface;
+                }
+                SAL_WARN_IF(renderMethodToUse() == RenderVulkan, "vcl.skia",
+                            "Cannot create Vulkan GPU offscreen surface, falling back to Raster");
+                SAL_WARN_IF(renderMethodToUse() == RenderMetal, "vcl.skia",
+                            "Cannot create Metal GPU offscreen surface, falling back to Raster");
+            }
+            break;
+        }
+        default:
+            break;
+    }
+    // Create raster surface as a fallback.
+    surface = SkSurface::MakeRaster(SkImageInfo::Make(width, height, type, alpha), surfaceProps());
+    assert(surface);
+    if (surface)
+    {
+#ifdef DBG_UTIL
+        prefillSurface(surface);
+#endif
+        return surface;
+    }
+    // In non-debug builds we could return SkSurface::MakeNull() and try to cope with the situation,
+    // but that can lead to unnoticed data loss, so better fail clearly.
+    abort();
+}
+
+sk_sp<SkImage> createSkImage(const SkBitmap& bitmap)
+{
+    SkiaZone zone;
+    assert(bitmap.colorType() == kN32_SkColorType || bitmap.colorType() == kAlpha_8_SkColorType);
+    switch (renderMethodToUseForSize(bitmap.dimensions()))
+    {
+        case RenderVulkan:
+        case RenderMetal:
+        {
+            if (GrDirectContext* grDirectContext = getSharedGrDirectContext())
+            {
+                sk_sp<SkSurface> surface = SkSurface::MakeRenderTarget(
+                    grDirectContext, SkBudgeted::kNo,
+                    bitmap.info().makeAlphaType(kPremul_SkAlphaType), 0, surfaceProps());
+                if (surface)
+                {
+                    SkPaint paint;
+                    paint.setBlendMode(SkBlendMode::kSrc); // set as is, including alpha
+                    surface->getCanvas()->drawImage(bitmap.asImage(), 0, 0, SkSamplingOptions(),
+                                                    &paint);
+                    return makeCheckedImageSnapshot(surface);
+                }
+                // Try to fall back in non-debug builds.
+                SAL_WARN_IF(renderMethodToUse() == RenderVulkan, "vcl.skia",
+                            "Cannot create Vulkan GPU offscreen surface, falling back to Raster");
+                SAL_WARN_IF(renderMethodToUse() == RenderMetal, "vcl.skia",
+                            "Cannot create Metal GPU offscreen surface, falling back to Raster");
+            }
+            break;
+        }
+        default:
+            break;
+    }
+    // Create raster image as a fallback.
+    sk_sp<SkImage> image = SkImage::MakeFromBitmap(bitmap);
+    assert(image);
+    return image;
+}
+
+sk_sp<SkImage> makeCheckedImageSnapshot(sk_sp<SkSurface> surface)
+{
+    sk_sp<SkImage> ret = surface->makeImageSnapshot();
+    assert(ret);
+    if (ret)
+        return ret;
+    abort();
+}
+
+sk_sp<SkImage> makeCheckedImageSnapshot(sk_sp<SkSurface> surface, const SkIRect& bounds)
+{
+    sk_sp<SkImage> ret = surface->makeImageSnapshot(bounds);
+    assert(ret);
+    if (ret)
+        return ret;
+    abort();
+}
+
+namespace
+{
+// Image cache, for saving results of complex operations such as drawTransformedBitmap().
+struct ImageCacheItem
+{
+    OString key;
+    sk_sp<SkImage> image;
+    tools::Long size; // cost of the item
+};
+} //namespace
+
+// LRU cache, last item is the least recently used. Hopefully there won't be that many items
+// to require a hash/map. Using o3tl::lru_map would be simpler, but it doesn't support
+// calculating cost of each item.
+static std::list<ImageCacheItem> imageCache;
+static tools::Long imageCacheSize = 0; // sum of all ImageCacheItem.size
+
+void addCachedImage(const OString& key, sk_sp<SkImage> image)
+{
+    static bool disabled = getenv("SAL_DISABLE_SKIA_CACHE") != nullptr;
+    if (disabled)
+        return;
+    tools::Long size = static_cast<tools::Long>(image->width()) * image->height()
+                       * SkColorTypeBytesPerPixel(image->imageInfo().colorType());
+    imageCache.push_front({ key, image, size });
+    imageCacheSize += size;
+    SAL_INFO("vcl.skia.trace", "addcachedimage " << image << " :" << size << "/" << imageCacheSize);
+    const tools::Long maxSize = maxImageCacheSize();
+    while (imageCacheSize > maxSize)
+    {
+        assert(!imageCache.empty());
+        imageCacheSize -= imageCache.back().size;
+        SAL_INFO("vcl.skia.trace",
+                 "least used removal " << imageCache.back().image << ":" << imageCache.back().size);
+        imageCache.pop_back();
+    }
+}
+
+sk_sp<SkImage> findCachedImage(const OString& key)
+{
+    for (auto it = imageCache.begin(); it != imageCache.end(); ++it)
+    {
+        if (it->key == key)
+        {
+            sk_sp<SkImage> ret = it->image;
+            SAL_INFO("vcl.skia.trace", "findcachedimage " << key << " : " << it->image << " found");
+            imageCache.splice(imageCache.begin(), imageCache, it);
+            return ret;
+        }
+    }
+    SAL_INFO("vcl.skia.trace", "findcachedimage " << key << " not found");
+    return nullptr;
+}
+
+void removeCachedImage(sk_sp<SkImage> image)
+{
+    for (auto it = imageCache.begin(); it != imageCache.end();)
+    {
+        if (it->image == image)
+        {
+            imageCacheSize -= it->size;
+            assert(imageCacheSize >= 0);
+            it = imageCache.erase(it);
+        }
+        else
+            ++it;
+    }
+}
+
+tools::Long maxImageCacheSize()
+{
+    // Defaults to 4x 2000px 32bpp images, 64MiB.
+    return officecfg::Office::Common::Cache::Skia::ImageCacheSize::get();
+}
+
+static o3tl::lru_map<uint32_t, uint32_t> checksumCache(256);
+
+static uint32_t computeSkPixmapChecksum(const SkPixmap& pixmap)
+{
+    // Use uint32_t because that's what SkOpts::hash_fn() returns.
+    static_assert(std::is_same_v<uint32_t, decltype(SkOpts::hash_fn(nullptr, 0, 0))>);
+    const size_t dataRowBytes = pixmap.width() << pixmap.shiftPerPixel();
+    if (dataRowBytes == pixmap.rowBytes())
+        return SkOpts::hash_fn(pixmap.addr(), pixmap.height() * dataRowBytes, 0);
+    uint32_t sum = 0;
+    for (int row = 0; row < pixmap.height(); ++row)
+        sum = SkOpts::hash_fn(pixmap.addr(0, row), dataRowBytes, sum);
+    return sum;
+}
+
+uint32_t getSkImageChecksum(sk_sp<SkImage> image)
+{
+    // Cache the checksums based on the uniqueID() (which should stay the same
+    // for the same image), because it may be still somewhat expensive.
+    uint32_t id = image->uniqueID();
+    auto it = checksumCache.find(id);
+    if (it != checksumCache.end())
+        return it->second;
+    SkPixmap pixmap;
+    if (!image->peekPixels(&pixmap))
+        abort(); // Fetching of GPU-based pixels is expensive, and shouldn't(?) be needed anyway.
+    uint32_t checksum = computeSkPixmapChecksum(pixmap);
+    checksumCache.insert({ id, checksum });
+    return checksum;
+}
+
+static sk_sp<SkBlender> invertBlender;
+static sk_sp<SkBlender> xorBlender;
+
+// This does the invert operation, i.e. result = color(255-R,255-G,255-B,A).
+void setBlenderInvert(SkPaint* paint)
+{
+    if (!invertBlender)
+    {
+        // Note that the colors are premultiplied, so '1 - dst.r' must be
+        // written as 'dst.a - dst.r', since premultiplied R is in the range (0-A).
+        const char* const diff = R"(
+            vec4 main( vec4 src, vec4 dst )
+            {
+                return vec4( dst.a - dst.r, dst.a - dst.g, dst.a - dst.b, dst.a );
+            }
+        )";
+        auto effect = SkRuntimeEffect::MakeForBlender(SkString(diff));
+        if (!effect.effect)
+        {
+            SAL_WARN("vcl.skia",
+                     "SKRuntimeEffect::MakeForBlender failed: " << effect.errorText.c_str());
+            abort();
+        }
+        invertBlender = effect.effect->makeBlender(nullptr);
+    }
+    paint->setBlender(invertBlender);
+}
+
+// This does the xor operation, i.e. bitwise xor of RGB values of both colors.
+void setBlenderXor(SkPaint* paint)
+{
+    if (!xorBlender)
+    {
+        // Note that the colors are premultiplied, converting to 0-255 range
+        // must also unpremultiply.
+        const char* const diff = R"(
+            vec4 main( vec4 src, vec4 dst )
+            {
+                return vec4(
+                    float(int(src.r * src.a * 255.0) ^ int(dst.r * dst.a * 255.0)) / 255.0 / dst.a,
+                    float(int(src.g * src.a * 255.0) ^ int(dst.g * dst.a * 255.0)) / 255.0 / dst.a,
+                    float(int(src.b * src.a * 255.0) ^ int(dst.b * dst.a * 255.0)) / 255.0 / dst.a,
+                    dst.a );
+            }
+        )";
+        SkRuntimeEffect::Options opts;
+        // Skia does not allow binary operators in the default ES2Strict mode, but that's only
+        // because of OpenGL support. We don't use OpenGL, and it's safe for all modes that we do use.
+        // https://groups.google.com/g/skia-discuss/c/EPLuQbg64Kc/m/2uDXFIGhAwAJ
+        opts.enforceES2Restrictions = false;
+        auto effect = SkRuntimeEffect::MakeForBlender(SkString(diff), opts);
+        if (!effect.effect)
+        {
+            SAL_WARN("vcl.skia",
+                     "SKRuntimeEffect::MakeForBlender failed: " << effect.errorText.c_str());
+            abort();
+        }
+        xorBlender = effect.effect->makeBlender(nullptr);
+    }
+    paint->setBlender(xorBlender);
+}
+
+void cleanup()
+{
+    sharedWindowContext.reset();
+    imageCache.clear();
+    imageCacheSize = 0;
+    invertBlender.reset();
+    xorBlender.reset();
+}
+
+static SkSurfaceProps commonSurfaceProps;
+const SkSurfaceProps* surfaceProps() { return &commonSurfaceProps; }
+
+void setPixelGeometry(SkPixelGeometry pixelGeometry)
+{
+    commonSurfaceProps = SkSurfaceProps(commonSurfaceProps.flags(), pixelGeometry);
+}
+
+// Skia should not be used from VCL backends that do not actually support it, as there will be setup missing.
+// The code here (that is in the vcl lib) needs a function for creating Vulkan/Metal context that is
+// usually available only in the backend libs.
+void prepareSkia(std::unique_ptr<sk_app::WindowContext> (*createGpuWindowContext)(bool))
+{
+    setCreateGpuWindowContext(createGpuWindowContext);
+    skiaSupportedByBackend = true;
+}
+
+void dump(const SkBitmap& bitmap, const char* file) { dump(SkImage::MakeFromBitmap(bitmap), file); }
+
+void dump(const sk_sp<SkSurface>& surface, const char* file)
+{
+    surface->getCanvas()->flush();
+    dump(makeCheckedImageSnapshot(surface), file);
+}
+
+void dump(const sk_sp<SkImage>& image, const char* file)
+{
+    sk_sp<SkData> data = image->encodeToData(SkEncodedImageFormat::kPNG, 1);
+    std::ofstream ostream(file, std::ios::binary);
+    ostream.write(static_cast<const char*>(data->data()), data->size());
+}
+
+#ifdef DBG_UTIL
+void prefillSurface(const sk_sp<SkSurface>& surface)
+{
+    // Pre-fill the surface with deterministic garbage.
+    SkBitmap bitmap;
+    bitmap.allocN32Pixels(2, 2);
+    SkPMColor* scanline;
+    scanline = bitmap.getAddr32(0, 0);
+    *scanline++ = SkPreMultiplyARGB(0xFF, 0xBF, 0x80, 0x40);
+    *scanline++ = SkPreMultiplyARGB(0xFF, 0x40, 0x80, 0xBF);
+    scanline = bitmap.getAddr32(0, 1);
+    *scanline++ = SkPreMultiplyARGB(0xFF, 0xE3, 0x5C, 0x13);
+    *scanline++ = SkPreMultiplyARGB(0xFF, 0x13, 0x5C, 0xE3);
+    bitmap.setImmutable();
+    SkPaint paint;
+    paint.setBlendMode(SkBlendMode::kSrc); // set as is, including alpha
+    paint.setShader(
+        bitmap.makeShader(SkTileMode::kRepeat, SkTileMode::kRepeat, SkSamplingOptions()));
+    surface->getCanvas()->drawPaint(paint);
+}
+#endif
+
+} // namespace
+
+#endif // HAVE_FEATURE_SKIA
+
+/* vim:set shiftwidth=4 softtabstop=4 expandtab: */